The objective of this study is to introduce a technique of far-field diversion using a mixture of soluble solid particles and an engineered proppant to ensure the temporarily bridged fractures re-open and remain propped for hydrocarbon flow after the soluble material has fully dissolved. Far-field diversion is required inside the fracture network to increase complexity by creating additional branch fractures through overcoming stresses holding the natural fractures closed. Usually, diverter particles temporarily bridge inside the fracture to create a low-permeability zone that increases the net pressure within the fracture and enables redirection of the next fluid stage to previously unstimulated intervals. However, if the diversion does not include proppant, the created fracture may close after particle dissolution.
The tests performed in this study were: bridging tests to determine the optimal particle size and loadings for a fracture width of 0.04 in.; pack permeability tests to optimize the particle size distribution, temporarily reduce fracture conductivity and increase pressure; and full characterization testing of the proppant as it will remain in the fractures after the soluble particles disappear. Conductivity of the proppant pack was also determined. Two types of particle diverters (Diverter A and B) were tested. Diverter A is typically used for low- to medium-temperature application (less than 225°F) and Diverter B for high-temperature applications (greater than 225°F). The two diverters have nearly the same particle size and distribution, the only difference being a variance in particle shape.
Results obtained highlighted reducing the proppant size to a larger mesh number to better place the proppant inside the far-field area with good vertical coverage. Therefore, the diverter particles were selected to be in the medium size range (10 to 50 mesh) while the proppant particles were selected to be in the fine size range (70 to 140 mesh). The crush stress at which the proppant generated less than 10 wt-% fines was 14,000 psi, while at 15,000 psi the proppant generated exactly 10 wt-% fines. The average acid solubility of this proppant in the mixture of HCl:HF was 3.4%, well below the 7% API requirements. A loading of 0.5 ppg of Diverter A was needed to bridge and plug the 0.04-in. slot width, while it needed only 0.25 ppga of Diverter B to plug the same width. Both diverters significantly reduced the conductivity of the test slot discs. After the soluble particles dissolved, conductivity was provided through the 100 mesh ceramic proppant pack that was not previously attainable because there was no proppant.